Process for producing polyorganosiloxane with solid-acid zirconium oxide catalyst

ABSTRACT

The method for producing polyorganosiloxane from at least one type of organosilicon compound having a siloxane unit or alkoxysilane by the equilibrating reaction involving cleavage and recombination of the silicon-oxygen bond as a method carried out in the presence of an acidic catalyst capable of giving the product in high productivity and yield, corrosive to the system to a limited extent, and remaining in the product to a limited extent or degrading product quality to a limited extent if it remains, wherein a solid, acidic zirconium oxide catalyst is used as the acidic catalyst.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producingpolyorganosiloxane using a solid, acidic zirconium oxide catalyst, moreparticularly a method for producing a polyorganosiloxane from at leastone type of organosilicon compound having a siloxane unit oralkoxysilane as a starting material in the presence of an acidiccatalyst, wherein a solid, acidic zirconium oxide catalyst is used asthe acidic catalyst to produce the polyorganosiloxane by theequilibrating reaction involving cleavage and recombination of thesilicon-oxygen bond.

2. Description of the Prior Art

Polyorganosiloxane has been widely used in the chemical industry becauseof its high resistance to heat, cold weather and radioactive ray,excellent electrical characteristics, and peculiar interfacialcharacteristics, e.g., low surface tension. Polymerization for producingpolyorganosiloxane is generally based on an equilibrating reactioninvolving cleavage/recombination of a siloxane chain present in a cyclicpolyorganosiloxane, low-molecular-weight linear polyorganosiloxane ororganoalkoxysilane in the presence of an acidic or basic catalyst, orhydrolysis and subsequent dehydration/condensation ofdichloroorganosilane, dialkoxydiorganosilane or the like.

In particular, an equilibrating reaction has been extensively employedbecause of low hazardousness of the starting material and easiness ofcontrolling polymerization degree of the product. This reaction has beenwidely used for various purposes, e.g., for reducing polymerizationdegree of polyorganosiloxane and introduction of a functional group, inaddition to polymerization. For example, the equilibrating reactionbetween polydimethylsiloxane and hexamethyldisiloxane can realize lowpolymerization degree. It can make cyclic polyorganosiloxane, whencontrolled at an elevated temperature and vacuum. Moreover, theequilibrating reaction between, e.g., a hydrolysis/condensation productof N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane anddimethylpolysiloxane in the presence of an alkali catalyst can producean amino-modified polysiloxane.

A number of materials have been proposed as the catalysts for theabove-described equilibrating reactions. They include those based onsulfuric acid, hydrochloric acid, a Lewis acid, sodium hydroxide,potassium hydroxide, tetramethyl ammonium hydroxide, butyl phosphoniumsilanolate, an amine and phosphonitrile halide. However, these catalystsare not highly efficient, because they need a neutralization step andremoval of the neutralization product for catalyst inactivation andremoval. Moreover, the recovered neutralization product is difficult torecycle, because of its incompatibility with a filtration aid,polysiloxane or the like, and is at present disposed by incineration orland filling.

The production processes which can replace the present processes, whichmassively discharge wastes, are increasing in the midst of theheightened requirements for environmental protection. In particular, useof an acidic catalyst is essential for production of polyorganosiloxane,which contains the ≡Si—H bond, because the bond is undesirably reactivein the presence of an alkali catalyst. An acidic catalyst should beincorporated at as high as 1 to 5 parts by volume per 100 parts byvolume of the starting material to secure a practical reaction rate.Therefore, it involves a disadvantage of massively discharging wastes.

Moreover, these acidic catalysts are very corrosive to metals, and thesystem needs expensive materials corrosion-resistant or lined.

Recently, polyorganosiloxanes have been going into materials forelectronic devices or the like, which need highly refined startingmaterials. However, the polyorganosiloxanes produced in the presence ofa conventional catalyst tend to have limited applications, because oftrace quantities of the catalyst, neutralization product, neutralizer orthe like remaining in the product.

Solid, acidic catalysts, e.g., zeolite, ion-exchanging resin,acid-activated acidic clay, have been proposed. However, fewconventional acidic catalysts have been massively used, because of thereaction rate being impractically low over them.

SUMMARY OF THE INVENTION

It is an object of the present invention to find out a catalyst forproduction of polyorganosiloxane from an organosilicon compoundcontaining the silicon-oxygen bond, high in productivity, giving theproduct in a high yield, corrosive to the system to a limited extent,and remaining in the product to a limited extent or degrading productquality to a limited extent if it remains, to solve the problemsinvolved in the conventional catalysts. It is another object to find outconditions under which the catalyst is used.

The inventors of the present invention have tested a number of acidiccatalysts for production of polyorganosiloxane from an organosiliconcompound containing the silicon-oxygen bond to solve the above problems,and found that a specific, acidic catalyst can give a high-qualitypolyorganosiloxane in high productivity and yield, achieving the presentinvention.

The first aspect of the present invention is a method for producingpolyorganosiloxane from at least one type of organosilicon compoundhaving a siloxane unit or alkoxysilane in the presence of an acidiccatalyst by the equilibrating reaction involving cleavage andrecombination of the silicon-oxygen bond, wherein a solid, acidiczirconium oxide catalyst is used as the acidic catalyst.

The second aspect of the present invention is the method of the firstaspect for producing polyorganosiloxane, wherein the equilibratingreaction is achieved continuously with at least one type oforganosilicon compound having a siloxane unit or alkoxysilane beingcontinuously supplied into a reactor containing the solid, acidiczirconium oxide catalyst and treated for a residence time of 10 minutesto 2 hours.

The third aspect of the present invention is the method of the firstaspect for producing polyorganosiloxane, wherein the equilibratingreaction is achieved batchwise with at least one type of organosiliconcompound having a siloxane unit or alkoxysilane being treated in areactor containing the solid, acidic zirconium oxide catalyst,incorporated at 0.01 to 100 parts by weight per 100 parts by weight ofat least one type of the organosilicon compound having a siloxane unitor alkoxysilane, for a residence time of 10 minutes to 100 hours.

The fourth aspect of the present invention is the method of the secondor third aspect for producing polyorganosiloxane, wherein theequilibrating reaction is carried out at −10 to 200° C.

The fifth aspect of the present invention is the method of the firstaspect for producing polyorganosiloxane, wherein at least one type oforganosilicon compound having a siloxane unit or alkoxysilane containshydrosilyl group.

The sixth aspect of the present invention is the method of the firstaspect for producing polyorganosiloxane, wherein the solid, acidiczirconium oxide catalyst is produced by the following steps:

-   -   (a) kneading aluminum hydroxide and/or hydrous oxide, zirconium        hydroxide and/or hydrous oxide, and a compound containing        sulfuric acid,    -   (b) forming the above mixture, and    -   (c) firing the formed product at a temperature at which zirconia        of the tetragonal structure is produced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 plots refractive index of the reaction products(polyorganosiloxanes) prepared in EXAMPLES or COMPARATIVE EXAMPLESagainst reaction time.

FIG. 2 presents the GPC chart of the reaction product(polyorganosiloxane) prepared in EXAMPLE 1.

FIG. 3 presents the GPC chart of the reaction product(polyorganosiloxane) prepared in COMPARATIVE EXAMPLE 1.

FIG. 4 presents the GPC chart of the reaction product(polyorganosiloxane) prepared in COMPARATIVE EXAMPLE 2.

FIG. 5 presents the GPC chart of the reaction product(polyorganosiloxane) prepared in COMPARATIVE EXAMPLE 3.

DETAILED DESCRIPTION OF THE INVENTION

The method of the present invention for producing polyorganosiloxaneusing a solid, acidic zirconium oxide catalyst is described in detailfor each item.

1. Organosilicon Compound Having a Siloxane Unit

The organosilicon compound having a siloxane unit for the presentinvention serves as a starting material for producing polyorganosiloxaneusing a solid, acidic zirconium oxide catalyst. These compounds includecyclic polyorganosiloxane and linear polysiloxane.

(1) Cyclic Polyorganosiloxane

The cyclic polyorganosiloxane for the present invention is representedby the chemical formula (1):

(wherein, R¹ and R² are each a monovalent organic, SH or hydroxyl group,or hydrogen atom; and “n” is an integer of 3 to 12).

The organic groups represented by R¹ and R² in the formula (1) include asubstituted or unsubstituted alkyl group of 1 to 100 carbon atoms,alkylene group of 1 to 100 carbon atoms, substituted or unsubstitutedalkoxy group of 1 to 100 carbon atoms and substituted or unsubstitutedaryl group of 1 to 100 carbon atoms. The unsubstituted alkyl groupsinclude methyl, ethyl, propyl, butyl and octyl. The unsubstituted alkoxygroups include methoxy, ethoxy, propoxy and butoxy, and aryl groupsinclude phenyl, tolyl, benzyl and phenylethyl. The substituted alkylgroups include —C₃H₆(C₂H₄O)_(a)(C₃H₆O)_(b)R³ (“a” and “b” are each aninteger of 0 to 100, where at least one of “a” and “b” is 1 or more; andR³ is an alkyl group of 1 to 8 carbon atoms or acyl group of 1 to 8carbon atoms, or hydrogen atom), carboxyalkylene,alkyloxycarbonylalkylene, acryloxyalkylene, methacryloxyalkylene,halogenated alkyl, sulfoalkylene and hydroxyalkylene. The substitutedalkoxy groups include alkoxyalkyleneoxy and halogenated alkoxy. Thespecific examples of the cyclic polyorganosiloxane represented by thechemical formula (1) include those represented by the chemical formulae(2) to (6):

The still more specific examples include hexamethylcyclotrisiloxane,octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane,dodecamethylcyclohexasiloxane and hexadecamethylcyclooctasiloxane.

A cyclic polyorganosiloxane for the present invention is transformedinto the linear one by ring-opening polymerization in the presence of asolid, acidic zirconium oxide catalyst. A cyclic polyorganosiloxane,when present alone, may be theoretically polymerized to have anextremely high polymerization degree, and it is necessary to stop thepolymerization step before an equilibrium is completely attained, inorder to secure a desired polymerization degree.

It should be noted that a cyclic polyorganosiloxane is also an objectiveproduct of the present invention, which is produced by the equilibratingreaction at an elevated temperature and vacuum in the presence of asolid, acidic zirconium oxide catalyst.

When a cyclotetrasiloxane containing a functional group is to beproduced, the following cyclic polyorganosiloxanes containing afunctional group, represented by one of the chemical formulae (7) to(13), are useful as the starting monomers.

(wherein, “a” is 0 to 100, and “b” is 0 to 100).(2) Linear Polysiloxane

The linear polysiloxane in the present invention is the compoundrepresented by the chemical formula (14):

(wherein, R is independently monovalent organic, SH or hydroxyl group,or hydrogen atom; and “n” is an integer of 1 to 1,000,000, inclusive).

The organic groups represented by R in the formula (14) include asubstituted or unsubstituted alkyl group of 1 to 100 carbon atoms,alkylene group of 1 to 100 carbon atoms, substituted or unsubstitutedalkoxy group of 1 to 100 carbon atoms and substituted or unsubstitutedaryl group of 1 to 100 carbon atoms. The unsubstituted alkyl groupsinclude methyl, ethyl, propyl, butyl and octyl. The unsubstituted alkoxygroups include methoxy, ethoxy, propoxy and butoxy, and aryl groupsinclude phenyl, tolyl, benzyl and phenylethyl. The substituted alkylgroups include —C₃H₆(C₂H₄O)_(a)(C₃H₆O)_(b)R³ (“a” and “b'are each aninteger of 0 to 100, where at least one of “a” and “b” is 1 or more; andR³ is an alkyl group of 1 to 8 carbon atoms or acyl group of 1 to 8carbon atoms, or hydrogen atom), carboxyalkylene,alkyloxycarbonylalkylene, acryloxyalkylene, methacryloxyalkylene,halogenated alkyl, sulfoalkylene and hydroxyalkylene. The substitutedalkoxy groups include alkoxyalkyleneoxy and halogenated alkoxy.

Of these, an organosilicon compound having a hydrosilyl group with atleast one of Rs being hydrogen atom is the compound for which thepresent invention is particularly useful, because a basic catalystcannot be used for its production.

The linear polysiloxane described above can be polymerized to have ahigh polymerization degree by an equilibrating reaction with a cyclicpolyorganosiloxane. Moreover, an equilibrating reaction may be used fortwo types of linear polysiloxanes of different polymerization degree toproduce a linear polysiloxane of intermediate polymerization degree. Forexample, a linear polyorganosiloxane of high polymerization degree canhave a decreased polyorganosiloxane by an equilibrating reaction with apolysiloxane of low polymerization degree, e.g., hexamethyldisiloxane.Moreover, an equilibrating reaction of linear polyorganosiloxane at anelevated temperature and vacuum can give a cyclic polyorganosiloxane andlinear polyorganosiloxane of decreased polymerization degree. Asdescribed above, a linear polyorganosiloxane is an objective product aswell as a starting material for the present invention.

(3) Silicone-Based Terminal Stopper

As described above, a cyclic polyorganosiloxane, when present alone, maybe theoretically polymerized in the presence of an acidic catalyst tohave an extremely high polymerization degree, and it is necessary tostop the polymerization step before an equilibrium is completelyattained. It is therefore difficult to control the reaction, and aterminal stopper is preferably used for the equilibrating reaction. Thepreferable terminal stopper components include siloxanes, e.g.,hexamethyldisiloxane, 1,1,3,3-tetramethyldisiloxane and1,3-divinyl-1,1,3,3-tetramethyldisiloxane. The starting materials forthese stopper components can be obtained by distillinghydrolysis/condensation products, e.g., dichlorodiorganosilane,dichloroorganosilane, chlorotriorganosilane and chlorodiorganosilane.The commercial products useful as a stopper include apolydimethylsiloxane (L-45 (10), Nippon Unicar, viscosity: 10mm²/second, number of silicon atoms: about 14 on the average).

A diorganopolysiloxane capable of stopping silanol chaining has afunction of terminal stopping. This compound is a linear silicone-basedpolymer, represented by the chemical formula (14), and having aviscosity of around 5 to 900 cP at 25° C., hydroxyl group at bothterminals and molecular weight of around several hundreds to thousands.

2. Alkoxysilane

The alkoxysilanes for the present invention meanstriorganomonoalkoxysilane represented by R⁴ ₃—Si—OR⁵,diorganodialkoxysilane represented by R⁴ ₂—Si—(OR⁵)₂,monoorganotrialkoxysilane represented by R⁴—Si—(OR⁵)₃, tetraalkoxysilanerepresented by Si—(OR⁵)₄ and the like.

In the above formulae, R⁴ is a monovalent organic or SH group, orhydrogen atom. The organic groups include a substituted or unsubstitutedalkyl group of 1 to 100 carbon atoms, alkylene group of 1 to 100 carbonatoms and substituted or unsubstituted aryl group of 1 to 100 carbonatoms. The unsubstituted alkyl groups include methyl, ethyl, propyl,butyl and octyl, and aryl groups include phenyl, tolyl, benzyl andphenylethyl. The substituted alkyl groups include—C₃H₆(C₂H₄O)_(a)(C₃H₆O)_(b)R³ (“a” and “b” are each an integer of 0 to100, where at least one of “a” and “b” is 1 or more; and R³ is an alkylgroup of 1 to 8 carbon atoms or acyl group of 1 to 8 carbon atoms, orhydrogen atom), carboxyalkylene, alkyloxycarbonylalkylene,acryloxyalkylene, methacryloxyalkylene, halogenated alkyl, sulfoalkyleneand hydroxyalkylene.

R⁵ is an alkyl group of 1 to 6 carbon atoms or alkoxyalkyl of 2 to 8carbon atoms. They include methyl, ethyl, propyl, butyl, hexyl andmethoxymethyl.

(1) Triorganomonoalkoxysilane

A triorganomonoalkoxysilane is a monofunctional, terminal-treating agent(producing a group represented by M), and can produce a linearpolyorganosiloxane by the equilibrating reaction with a cyclicpolyorganosiloxane.

More specifically, triorganomonoalkoxysilanes includetrimethylmethoxysilane, triethylethoxysilane, triphenylmethoxysilane andtriphenylethoxysilane.

(2) Diorganodialkoxysilane

A diorganodialkoxysilane is a difunctional compound (producing a grouprepresented by D), and can serve as a monomer copolymerizable with acyclic polyorganosiloxane.

More specifically, diorganodialkoxysilanes includedimethyldimethoxysilane, diethyldimethoxysilane, dimethyldiethoxysilane,diethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane,methylphenyldimethoxysilane, methylphenyldiethoxysilane,ethylphenyldimethoxysilane and ethylphenyldiethoxysilane.

When a polysiloxane containing a functional group is to be produced, thefollowing dialkoxysilanes containing a functional group, represented byone of the chemical formulae (15) to (21), are useful as the startingmonomers.

(wherein, “a” is 0 to 100, and “b” is 0 to 100).(3) Monoorganotrialkoxysilane

A monoorganotrialkoxysilane is a trifunctional compound (producing agroup represented by T), and can produce a branched polyorganosiloxaneby an equilibrating reaction with a cyclic polyorganosiloxane.

Monoorganotrialkoxysilanes useful for the present invention includemethyltrimethoxysilane, ethyltriethoxysilane, phenyltrimethoxysilane andphenyltriethoxysilane.

When a polysiloxane containing a functional group is to be produced, thefollowing trialkoxysilanes containing a functional group, represented byone of the chemical formulae (22) to (28), are useful as the startingmonomers.

(wherein, “a” is 0 to 100, and “b” is 0 to 100).(4) Tetraalkoxysilane

A tetraalkoxysilane is a tetrafunctional compound (producing a grouprepresented by Q), and can produce a branched polyorganosiloxane by anequilibrating reaction with a cyclic polyorganosiloxane.

Tetraalkoxysilanes useful for the present invention includetetramethoxysilane, tetraethoxysilane, tetrabutoxysilane andtetrapropoxysilane.

3. Solid, Acidic Zirconium Oxide Catalyst

A solid, acidic zirconium oxide catalyst for the present invention maybe a known one. For example, it may be prepared by a process involvingtreatment of zirconium hydroxide with sulfuric acid and subsequentfiring at 300° C. or higher. It is particularly preferable to use thesolid, acidic zirconium oxide catalyst prepared by a process involvingthe following steps:

-   -   (a) kneading aluminum hydroxide and/or hydrous oxide, zirconium        hydroxide and/or hydrous oxide, and a compound containing        sulfuric acid,    -   (b) forming the above mixture, and    -   (c) firing the formed product at a temperature at which zirconia        of the tetragonal structure is produced, because of its high        catalytic activity and easiness of separation after it is used        for the reaction. The method for producing the catalyst is        known, as disclosed by, e.g., WO98/09727. It is particularly        preferable when formed into particles or pellets of around 1 mm        in size. One of the commercial catalysts suitably used is SZA-60        (Japan Energy).        4. Method for Producing Polyorganosiloxane

The polyorganosiloxane for the present invention is produced by theequilibrating reaction of at least one type of organosilicon compoundhaving the above-described siloxane unit or alkoxysilane in the presenceof a solid, acidic zirconium oxide catalyst. The reaction may be carriedout either continuously or batchwise.

The equilibrating reaction means the reaction in which at least one typeof organosilicon compound having the siloxane unit is or alkoxysilane asa starting material treated in the presence of an acidic catalyst toproduce a polyorganosiloxane of new molecular weight distribution bycleavage and recombination of the silicon-oxygen bond.

When the equilibrating reaction is carried out batchwise, an adequatequantity of the starting material for polyorganosiloxane undergoes thereaction in the presence of an adequate quantity of the catalyst withstirring in a reactor. On completion of the reaction, the catalyst isseparated from the reaction mixture, and the product is separated fromthe reaction mixture.

When the equilibrating reaction is carried out continuously, thestarting material is continuously charged into a slurry reactor withbackmixing, where it is continuously stirred, and the effluent isdischarged also continuously. It may be also carried out in a pipelinereactor, where the starting material moves in a plug flow through thereactor filled with the catalyst. The movement is characterized by plugflow, where the starting material is converted as it moves, withessentially no mixing with the starting material from the startingmaterial partly converted.

The pipeline reactor is preferably oriented vertically, because thereaction stream moving upwards while passing over the catalyst has anincreased freedom of flow. It may move downwards, which, however,compresses the catalyst and tends to limit its freedom of flow.

It is preferable to control the reaction conditions, e.g., temperatureand product concentration in the reaction zone, and reaction time bycontrolling flow rate of the reaction stream into or out of the reactionzone, whether the reactor is of slurry or pipeline type.

Residence time in a continuous reactor, i.e., reaction time realized bycontrolling flow rate of the reaction stream into or out of the reactionzone, is preferably 10 minutes to 2 hours, more preferably 15 to 60minutes, still more preferably 20 to 45 minutes. It can be determined bydividing the free volume (mL) determined by measuring in the reactionzone by flow rate (mL/minute) of the reaction stream passing through thereactor. The reaction zone is the whole volume of the reaction mixturein the case of a slurry reactor, and the zone filled with the catalystin the case of a pipeline reactor.

In the batch system, the catalyst is incorporated preferably at 0.01 to100 parts by weight per 100 parts by weight of at least one type oforganosilicon compound having a siloxane unit or alkoxysilane as thestarting material, more preferably 0.1 to 50 parts, still morepreferably 1 to 10 parts. Reaction time for the equilibrating reactionis preferably 10 minutes to 100 hours, more preferably 1 to 10 hours.

The reaction may be carried out generally at the normal pressure,whether in a batch or continuous system. It may be also carried out at avacuum or elevated pressure, in order to control the reactionconditions, e.g., reaction time and temperature of the reaction mixture.Reaction temperature is preferably −10 to 200° C., more preferably 10 to80° C., still more preferably 20 to 65° C. The reaction rate isinsufficient when it is below the above range. At a temperature beyondthe above range, on the other hand, the siloxane chain will becomeunstable, retarding the silicon-oxygen recombination reaction, with theresult that the objective product may be difficult to produce, in spiteof the increased cost for heating. Therefore, a reaction temperature outof the above range is not desirable.

On completion of the equilibrating reaction, the catalyst is separatedfrom the reaction mixture by an adequate means, e.g., filtration,decantation or centrifugal separation, to be reused. In the continuoussystem, the catalyst is simply retained in the reactor, to which thefresh reaction stream is charged and from which the product isdischarged.

After the catalyst is separated, the residual, unreacted startingmixture may be extracted from the reaction mixture by distillation orstripping with an inert gas, e.g., steam or nitrogen, whether thereaction system is operated batchwise or continuously.

EXAMPLES

The present invention is described in more detail by EXAMPLE, which byno means limits the present invention. The GPC analysis was carried outin EXAMPLE and COMPARATIVE EXAMPLES for the products or the like by thefollowing procedure.

GPC analysis:

Number-average molecular weight (Mn) was determined by gel permeationchromatography (GPC) under the following conditions.

Analyzer: GPC analysis system (JASCO)

Column: Shodex-803L (Showa Denko)

Detector: Refractive index (RI) detector RL540 R (GL Science)

Calibration curve: A total of 10 types of standard polystyrene(molecular weight: 1.2×10³ to 2.75×10⁶, Showa Denko) was used to preparethe calibration curve.

Measurement: Chloroform was passed at 1.0 mL/minute at 40° C., intowhich 100 μL of the sample (concentration: 0.3% by weight) was injected.

Example 1

A flow reactor system equipped with a pressure gauge was assembled byconnecting a pump, reactor tower (inner diameter: 15 mm), back-pressurevalve and Erlenmeyer flask (500 ml) equipped with a magnetic stirrer, inthis order. The reactor tower was charged with 20 mL of zirconia sulfate(SZA-60, Japan Energy) as a solid, acidic zirconium oxide catalyst, andsealed with glass wool at both ends. The zirconia sulfate was slightlycrushed in a mortar to have a uniform size of 10 to 20 meshes, and firedat 350° C. in an oven for 2 hours just before it was charged into thereactor.

The Erlenmeyer flask was charged with 290 mL of a mixture of 7.87% byweight of hexamethyldisiloxane (Me₃SiOSiMe₃), 42.86% by weight of methylhydrogen polysiloxane (Me₃Si[OSi(H)(Me)]₃₇OSiMe₃, L-31, Nippon Unicar)and 49.27% by weight of octamethylcyclotetrasiloxane (SiMe₂O)₄, Y-7175,Nippon Unicar) as the starting mixture well-mixed beforehand to beuniform. The mixture was circulated at 67 g/hour in the reactor system,with stirring at 25° C. About 3 mL of the reaction solution waswithdrawn from the flask by syringe at intervals of several hours, to beanalyzed for refractive index and by GPC. FIG. 1 plots refractive indexof the reaction solution against reaction time of up to 75 hours. FIG. 2shows the GPC charts of the initial solution, and the solutionsundergoing the reaction for 6 and 30 hours. It was observed thatrefractive index of the reaction solution reached a constant level inabout 6 hours (FIG. 1), and that the solutions undergoing the reactionfor 6 and 30 hours had almost the same GPC patterns (FIG. 2), and hadalmost the same molecular weights of the peak component flowing out in aretention time of 15 to 20 minutes. It is therefore considered, based onthese results, that an equilibrium is attained in about 6 hours.

It is therefore found that the equilibrating reaction proceeds, wherebya compound having a molecular weight intermediate between those ofhexamethyldisiloxane and methyl hydrogen polysiloxane (L-31) istransformed into a linear polyorganosiloxane of higher polymerizationdegree in the presence of octamethylcyclotetrasiloxane.

Comparative Example 1

The test was carried out for up to 33 hours in the same manner as inEXAMPLE 1, except that the catalyst was replaced by zeolite β(HSZ-930HOD1A, Tosoh), to measure refractive index and GPC-determinedmolecular weight of the reaction solution. FIG. 1 plots refractive indexof the reaction solution against reaction time. As shown, refractiveindex of the solution changes little with time even for 33 hours, atwhich the test was stopped because of no symptom of change anticipated.FIG. 3 shows the GPC charts of the initial solution, and the solutionsundergoing the reaction for 27 and 33 hours. As shown, these solutionshad almost the same GPC patterns. They had almost the same molecularweights of the peak component flowing out in a retention time of 15 to20 minutes. It is therefore considered that no reaction proceeds in thissystem.

Comparative Example 2

The test was carried out for 267 hours in the same manner as in EXAMPLE1, except that the catalyst was replaced by a strongly acidic,cation-exchanging resin (Amberlist 36, Organo), to measure refractiveindex and GPC-determined molecular weight of the reaction solution. FIG.1 plots refractive index of the reaction solution against reaction time.FIG. 4 shows the GPC charts of the initial solution, and the solutionsundergoing the reaction for 195 and 267 hours. As shown in FIG. 1,refractive index of the solution continued to change for 267 hours,indicating that an equilibrium was not attained for this time period.The GPC pattern also continued to change for 195 and 267 hours (FIG. 4),and so did molecular weight of the peak component flowing out in aretention time of 15 to 20 minutes, also indicating that an equilibriumwas not attained for 267 hours. To conclude: the reaction of this systemdoes proceed but at a low rate, taking a fairly long time (around 300hours) to attain an equilibrium.

Comparative Example 3

A 1 L kettle was charged with 500 g of the starting mixture of the samecomposition as that used in EXAMPLE 1, which was stirred at 25° C. andatmospheric pressure for 12 hours in a nitrogen atmosphere in thepresence of 25.0 g (2.5 pph) of concentrated sulfuric acid as thecatalyst. The effluent was incorporated with 125 g (12.5 pph) of sodiumhydrogen carbonate NaHCO₃ and stirred for 4 hours for neutralization.The effluent was filtered through filter paper under pressure, and thefiltrate was recovered as the product. It was analyzed for itsrefractive index and GPC-determined molecular weight. The refractiveindex was 1.3974 and molecular weight was 2700. FIG. 5 shows the GPCcharts of the initial solution and the solution undergoing the reactionfor 4 hours. These patterns were similar to those prepared in EXAMPLE 1.Molecular weight of the peak component flowing out in a retention timeof 15 to 20 minutes was also the same as that prepared in EXAMPLE 1.Therefore, the reaction system attained an equilibrium in 4 hours. Thereaction was similar in equilibrium kinetics to that observed in EXAMPLE1, but produced much more wastes.

The method of the present invention for producing polyorganosiloxane hasvarious favorable effects, e.g., giving the high-quality productcontaining only limited quantities of impurities at a high reaction ratein high productivity and yield, suffering corrosion of the productionsystem to only a limited extent, operating for extended periodscontinuously without shut-down for repair and without replacing thecatalyst to reduce the production cost.

1. A method for producing polyorganosiloxane from at least one type oforganosilicon compound having a siloxane unit or alkoxysilane in thepresence of an acidic catalyst by the equilibrating reaction involvingcleavage and recombination of the silicon-oxygen bond, wherein a solid,acidic zirconium oxide catalyst is used as the acidic catalyst.
 2. Themethod for producing polyorganosiloxane according to claim 1, whereinthe equilibrating reaction is achieved continuously with at least onetype of the organosilicon compound having a siloxane unit oralkoxysilane being continuously supplied into a reactor containing thesolid, acidic zirconium oxide catalyst and treated for a residence timeof 10 minutes to 2 hours.
 3. The method for producing polyorganosiloxaneaccording to claim 1, wherein the equilibrating reaction is achievedbatchwise with at least one type of the organosilicon compound having asiloxane unit or alkoxysilane being treated in a reactor containing thesolid, acidic zirconium oxide catalyst, incorporated at 0.01 to 100parts by weight per 100 parts by weight of at least one type of theorganosilicon compound having a siloxane unit or alkoxysilane, for aresidence time of 10 minutes to 100 hours.
 4. The method for producingpolyorganosiloxane according to claim 2 or 3, wherein the equilibratingreaction is carried out at −10 to 200° C.
 5. The method for producingpolyorganosiloxane according to claim 1, wherein at least one type ofthe organosilicon compound having a siloxane unit or alkoxysilanecontains hydrosilyl group.
 6. The method for producingpolyorganosiloxane according to claim 1, wherein the solid, acidiczirconium oxide catalyst is produced by the following steps: (a)kneading aluminum hydroxide and/or hydrous oxide, zirconium hydroxideand/or hydrous oxide, and a compound containing sulfuric acid, (b)forming the above mixture, and (c) firing the formed product at atemperature at which zirconia of the tetragonal structure is produced.